> There is no way for a forwarded email to SASL authenticate because no one is logged in or involved in the process of LMTP receiving mail for delivery from "the world". How is the MTA supposed to know the SASL password for staff@work.com?

dovecot auth with "master user" when sending emails via sumbission_host;
postfix:
1. using smtpd_sender_login_maps allow master user send messages with any mail from, like that:
smtpd_sender_login_maps = regexp:/etc/postfix/login_map.regexp
---
login_map.regexp:
/^master@example.com$/ .*

OR

2. in postfix master.cf declare dedicatet submission port allowed only for dovecot, without reject_sender_login_mismatch, like that:
2525       inet  n       -       n       -       -       smtpd         
   -o smtpd_helo_restrictions=permit_sasl_authenticated                          
   -o smtpd_relay_restrictions=permit_sasl_authenticated,reject                        
   -o smtpd_sender_restrictions=permit_sasl_authenticated

I think it's better than
mynetworks = 10.0.1.0/24 #whole subnet, container ip assigned dynamically :(
with
smtpd_sender_restrictions =
   permit_mynetworks
smtpd_relay_restrictions =
   permit_mynetworks

What about SPF in the described scenario, you are right, SPF will be broken. Well.. its implementation feature




От: dovecot <dovecot-bounces@dovecot.org> от имени dovecot@ptld.com <dovecot@ptld.com>
Отправлено: 17 января 2023 г. 23:18
Кому: dovecot@dovecot.org <dovecot@dovecot.org>
Тема: Re: submission_host auth
 
> Let's say we have dovecot + sieve plugin container.
> Dovecot configured to use remote SMTP submission host to send messages:
> submission_host = postfix.example.com:587


I reviewed my config to see how i did it. I think you are right and SASL isn't used here. I have dovecot and postfix on the same machine and in dovecot i set
     submission_host = localhost:25

Then in my sieve filters i set
     sieve_redirect_envelope_from = sender

I use SPF, DKIM, and DMARC

To test this i have (fictitious) staff@work.com with a forward filter to personal@home.com
I sent an email from customer@random.com to staff@work.com
@work.com server then sends a forwarded email to personal@home.com with To:staff@work.com and From:customer@random.com

Checking the @home.com logs i can see that SPF failed because @work.com server sent an email from @random.com, however it had valid DKIM signatures from both @work.com and @random.com so DMARC passed and the email was accepted.

I guess if the @random.com mail server only implemented SPF and not included a DKIM signature and DMARC policy then the @home.com server would have rejected the forwarded email.

I know this might not be the best solution you are looking for, but it is the best i could figure out to allow sieve forwarding. There is no way for a forwarded email to SASL authenticate because no one is logged in or involved in the process of LMTP receiving mail for delivery from "the world". How is the MTA supposed to know the SASL password for staff@work.com?